Design of feedback controller for non-minimum phase nano positioning system

Abstract

One of the most important requirement of nanotechnology is precision control and manipulation of devices and materials at nanoscale i.e. nanopositioning. Nanopositioners are precision mechatronic system designed to move objects over a small range with a resolution down to a fraction of an atomic diameter. In particular, desired specifications of any nanopositioners are fast response with no or very little overshoot, large travel range with very high resolution, extremely high precision and high bandwidth. This paper presents design and identification of nanopositioning device consisting of flexure stage, piezoelectric actuator and Linear Variable Differential Transformer (LVDT) as a sensor. Open loop behavior of the nanopositioning device on the basis of time and frequency responses is studied. To improve the system characteristics feedback controllers are used. Step response and frequency response under variety of conditions are obtained to verify the effectiveness of the proposed controllers. In this paper PI and PI2 controllers are designed and system performances are investigated for different values of feedback gain. Unfortunately nanopositioners operating in closed loop achieve high bandwidth at the cost of increased sensitivity to the measurement noise and hence reduced resolution. In this paper H infinity controller is analyzed and performance of the device is studied. Then a comparative study of traditional PI and PI2 controller with H infinity controller on the basis of time and frequency response is given to show which controller is better. Simulation results for the performance analysis are carried out in MATLAB. © 2013 VBRI press.